Paranormal investigator and cryptozoologist Joe Nickell has spent 40 years doing fieldwork and research, digging for the truth behind bizarre phenomena like weeping statues and haunted houses. He invited us to his office to talk about the connections between Bigfoot and alien mythology, life as the token skeptic on TV, and why debunkers are just as bad as mystery mongers.

Joe Nickell is perhaps the world's only full-time salaried paranormal investigator. "I'm terrible at catching ghosts," he told me with a wry smile. "I have a pitiful record when it comes to catching extraterrestrials." His jovial manner belies the stereotype of the dour skeptic, and he delights in showing off his collection of curios and oddities gathered in the course of his work as senior research fellow for the Committee for Skeptical Inquiry and author of the "Investigative Files" column for Skeptical Inquirer.

He gets very serious, however, when I bring up accusations that he destroys a sense of wonder in the world. "We should look for the truth because the truth matters," he says, "and we should face reality because, well – we can look at the Dark Ages and see where it gets us if we don't. The idea that we shouldn't solve mysteries is foreign to the human experience. The progress of science is a series of solved mysteries."

When it came time to talk cryptids, we started with the most famous, the "Bigfoot" depicted in the infamous Patterson film. Nickell has researched the issue and even befriended costume maker Phillip Morris, who claims he made a gorilla suit for Patterson shortly before the film was made. Corroborating this testimony is Bob Heironimus, who says he was the man wearing the suit in the footage. Finally, analysis reveals that the creature in the image looks like a man in a fake fur suit in many ways. "There's an odd double-standard in that people subject the hoax claims to a high degree of skepticism without being as skeptical of some of the outlandish theories about the creature," Nickell said.

While researching his 2011 book Tracking the Man-beasts, he found a previously published catalogue of North American Sasquatch sightings. By organizing the sightings and their major characteristics into a continuum arranged by date and location, he was able to see patterns, and a fascinating theory emerged. At first, the creatures showed enormous variation in color, height, behavior, foot size and even number of toes. To suggest a single undiscovered hominid living in the North American wilderness was one thing. To suppose that dozens of different species existed, many of them in relatively populated places like Illinois and New jersey, "strains credulity," as Nickell put it.

Then the Patterson film was made in 1967. It attracted widespread publicity and was shown on popular national talk shows. From that point forward, variations in Sasquatch sightings began to dwindle. Creatures sighted after the release of the Patterson film exhibited a great tendency to resemble the creature depicted in the film.

This clued Nickell in to an amazing phenomenon – the Patterson film represented the current and ongoing development of a modern mythology. He traces the myth's origins to popularization of Yeti stories in American men's magazines in the 1950s. The myth's shape was largely defined by the Patterson footage, and from then on sightings hewed closely to the myth as it had been established in the public's mind.

"We have a propensity to create man-beasts in our own image. You can see this in the hybrid human-animal creatures of Egyptian mythology and other ancient panoplies," Nickell said. "Bigfoot is our stupid cousin from the past. The alien is the future version of ourselves." In fact, tracing the iconography of aliens yielded similar results to the Bigfoot study. Using a published catalogue of reports of alien encounters (avoiding selection bias which may have appeared if he chose the cases himself), Nickell found, again, a wide variety in the morphology of sighted alien creatures. In 1966, the Betty and Barney Hill abduction case was publicized with a book on the case and front page newspaper articles (the incident itself had occurred in 1961). The hills described short, gray-skinned aliens with large heads and eyes. These same aliens started appearing in other sightings from that point on, until the late 1980s, when a confluence of cultural influences cemented that form of alien into the public consciousness. Virtually every major alien sighting from 1990 onward depicts a "Gray." The same convergent iconography can be seen in artists' depictions of Jesus Christ and Santa Clause.

What about cryptids that aren't shaped like humans? The most common are lake monsters like Nessie and dozens of others around the world. Nickell has a convincing argument based, again, on data mapping. He plotted the distribution of North American lake monster sightings. Then he overlaid the distribution of the common otter and found a near perfect match. It turns out that three or four otters swimming in a line look remarkably like a serpentine, humped creature undulating through the water. It is very easy to mistake for a single creature if you see them from a distance. "This isn't speculation. I'm not making this up," Nickell said. "I've spoken to people who saw what they thought was a lake monster, got closer and discovered it was actually a line of otters. That really happens." Clearly, not every lake monster sighting can be accounted for with otters, but it's an excellent example of how our perceptions can be fooled.

Nickell doesn't confine his research to data analysis. He has traveled around the world and spent a great deal of time doing field research. "I've found that I have more in common with the cryptozoologists out there in the woods than with the armchair skeptics." At all times, Nickell emphasizes that he is not a debunker, and he goes to great lengths to eliminate bias from his work. His goal is to examine the evidence, whatever it may be, and find the most logical, reasonable truth that the evidence points to. He chides skeptics who are dismissive or even derogatory toward eyewitnesses. "I've spoken with many witnesses, and they are sane, intelligent, sober, honest people who have seen something that, yes maybe they've mistaken for something else, but even skeptics have been mistaken." (Nickell reserved no such respect for frauds and hoaxers, however).

I asked Nickell about the equipment he brings along when he does field research. He uses a series of kits packed into compact plastic bins, each one containing a specific set of gear. This way, he can use a modular approach and bring along whatever kits are best for the job at hand. He typically has evidence collection bags, swabs, camera and a magnifier with him at all times, but he might also have a stereo microscope, more robust collection materials and other tools of the trade. When in the wilderness for cryptid investigations, Nickell travels light, but he does have the necessary equipment to make plaster casts of footprints when necessary.

Television producers frequently ask Nickell to appear in documentaries on paranormal subjects, usually as the "token skeptic." Despite the fact that they often twist his words or take his quotes out of context, he continues to make such appearances in hopes that getting some skeptical thought on the air is better than none. To provide an idea of the attitude that these production companies hold, he relates a story about an episode of MonsterQuest filmed in Montreal about unidentified flying humanoids. The segment producer took him for out for dinner and a few drinks that evening and told him, "When I asked the MonsterQuest production head if I could use Joe Nickell in this episode, he said, ‘Sure, but hopefully he won't be too convincing this time.'" Another time, Nickell was asked to describe the legend of the Hope Diamond Curse, which he did enthusiastically. Then he was asked to explain why he thought the curse wasn't real. They included only the first half, making it seem as if he wholeheartedly believed in the curse.

"Don't get your science from crappy TV shows," Nickell said. "If someone has convincing findings, it will appear in one of the science journals. These paranormal shows are as real as wrestling."